Biofloc technology (BFT) promotes nutrient recycling through microbe-mediated carbon–nitrogen transformations. However, the roles of heterotrophic and nitrifying bacteria in biofloc systems remain incompletely understood. This study examined the effects of microbial inoculation on carbon–nitrogen dynamics, biofloc development, water quality, and production performance in Nile tilapia (Oreochromis niloticus). Four treatments were evaluated: a natural microbial community (BFT1), a Bacillus consortium (BFT2), a nitrifying consortium (BFT3), and a combined consortium (BFT4). Fish were reared for 35 days following a 10-day biofloc maturation period. The treatments showed different patterns of carbon and nitrogen dynamics and production performance. BFT2 exhibited the largest biofloc volume (28 mL/L), the highest growth rate (GR = 0.696 g/day/fish), and the lowest feed conversion ratio (FCR = 1.10). BFT3 showed the highest nitrogen assimilation estimate (Nass = 385.05 mg/L), survival rate (SR = 91.67%), and harvested biomass (Hf = 646.37 g). BFT4 exhibited the highest apparent carbon consumption (Ccon = 624.32 mg/L), the lowest residual carbon concentration (Cyield = 167.01 mg/L), and the lowest calculated C/N ratio (4.42). Adding bacterial consortia was also associated with lower NH4+ and NO2− concentrations than those observed in BFT1. Overall, the different microbial inoculation treatments were associated with distinct carbon–nitrogen dynamics and production outcomes.
Crop response to nitrogen (N) fertilizer varies across space and time due to complex interactions among soil properties, weather, water availability, crop characteristics, and management practices, making the response to additional N difficult to predict. This variability presents a major challenge for N management because measurements of soil or crop N status do not necessarily indicate whether additional N will increase crop yield or quality. In intensive vegetable systems, short production cycles, frequent irrigation or fertigation, relatively shallow rooting in some crops, and high-value crops create narrow margins between insufficient and excessive N supply. The objectives of this critical review were to (i) examine how N supply, transformations and losses, water dynamics, root acquisition, and dynamic crop N demand generate variation in N response within genotype (crop) × environment × management (G × E × M) interactions; (ii) evaluate the capacity and limitations of soil and plant diagnostics, remote sensing, process-based models, and data-driven approaches to predict N response; (iii) identify factors limiting the transferability of N-response predictions; and (iv) define research priorities for predicting the marginal crop response to additional N and its uncertainty. This review identifies interactions among indigenous N supply, N transformations, soil water, root acquisition, and dynamic crop demand as major sources of variation in fertilizer response. Although soil and plant diagnostics, remote sensing, process-based models, and data-driven approaches provide valuable information about N status and crop performance, their capacity to predict the marginal yield or quality response to additional N remains constrained by incomplete process representation and limited counterfactual evidence. Prediction transferability is further limited by variation in G × E × M conditions, highlighting the need for response-generating experiments, improved representation of soil–plant–water interactions, explicit quantification of uncertainty, and independent validation across environments.
Nitrogen is a major challenge in zero-water-exchange (ZWE) aquaculture systems. This study examined the effects of dietary β-glucan and nucleotides on nitrogen transformation dynamics, oxidative stress responses, and environmental stability in Nile tilapia (Oreochromis niloticus). A 42-day feeding trial was conducted using diets supplemented with β-glucan (βg1 = 1%, βg2 = 2%, βg3 = 3%) and nucleotides (Nt1 = 1%, Nt2 = 2%, Nt3 = 3%). Final fish weight increased from 21.57 g in the control (Ct) to 28.32 g in Nt3. Total nitrogen (TN) derived from cumulative feed input reached 264.08 mg/L in Ct, whereas nucleotide treatments showed lower accumulation. NH4+ peaked between days 10 and 17, reaching 12.38 mg/L in Nt3, while NO2− peaked at 0.240 mg/L in Nt1 and declined to 0.03–0.07 mg/L by day 42. NO3− accumulated continuously to 31.74–51.47 mg/L, with higher concentrations generally observed in nucleotide treatments. Kinetic modeling yielded higher model-derived apparent nitrogen transfer coefficient (ka) in β-glucan treatments (1.287–1.690/day) and higher model-derived apparent nitrite-to-nitrate conversion coefficients (k2) in nucleotide treatments (4.994–5.748/day). Nucleotide supplementation favored apparent nitrite-to-nitrate conversion, whereas β-glucan was associated with greater apparent transfer of ammonia-derived nitrogen toward the modeled residual nitrogen pool.
After the liver, the gastrointestinal tract is a major and chemically versatile site of nitrogen transformation. Its microbiota processes endogenous and dietary nitrogenous substrates (proteins, peptides, amino acids, urea, choline and mucin-derived amino sugars) alongside diverse organic nitrogenous xenobiotics: azo and nitroaromatic drugs, food and textile colorants, heterocyclic aromatic amines from cooked meat, nitrosamines and drug-substance impurities, environmental nitroaromatics, and nitrogen-containing drugs such as levodopa and metronidazole. Because the colonic lumen is largely anoxic and strongly reducing, this chemistry is in several respects the mirror image of hepatic cytochrome P450 oxidation. Instead, azo bond cleavage, stepwise nitro group reduction, N-oxide reduction, hydrolysis of glucuronide conjugates, decarboxylation, deamination, dehydroxylation and O-demethylation dominate. The resulting metabolites may be therapeutically essential (5-aminosalicylic acid from sulfasalazine), pharmacologically detrimental (premature decarboxylation of levodopa), or genotoxic (aromatic amines, hydroxylamines, N-nitroso compounds). This review integrates the endogenous and xenobiotic branches of gut nitrogen metabolism, which share the same enzymes, cofactors and redox constraints and are inseparable in vivo. We summarize the enzymology underlying each transformation, the determinants of inter-individual variability, and emerging strategies (selective enzyme inhibitors, engineered strains, dietary and formulation-based interventions) that aim to steer the fate of nitrogenous xenobiotics towards benefit rather than harm. Throughout, we distinguish explicitly between evidence obtained in humans, in animal models, in defined bacterial isolates and in vitro systems, and mechanisms that are currently only chemically plausible. The novelty of this review lies in integrating the endogenous nitrogen economy of the gut with the biotransformation of nitrogenous xenobiotics as one system governed by shared enzymes, cofactors and redox constraints, rather than in surveying either field separately.
Nitrogen management is an important component of legume-based agroforestry, particularly where mineral nitrogen inputs and biological nitrogen acquisition interact. The present study evaluated contrasting mineral nitrogen and Rhizobium management treatments in a shisham (Dalbergia sissoo Roxb.)–jack bean (Canavalia ensiformis (L.) DC.) agroforestry system under the semi-arid conditions of Bundelkhand, India. The experiment was conducted during 2022–2023 and 2023–2024 at the Forestry Research Farm, Rani Lakshmi Bai Central Agricultural University (RLBCAU), Jhansi, India, using six treatments in a randomized complete block design with four replications. The present study evaluated the effects of contrasting mineral N levels and Rhizobium inoculation on jack bean growth, yield, nodulation and N uptake, together with shisham growth and soil N status, under a semi-arid agroforestry system. The treatments comprised sole jack bean with 0 and 100% recommended nitrogen, shisham–jack bean with 0, 50 and 100% recommended nitrogen, and Rhizobium-inoculated shisham–jack bean without mineral nitrogen. Nitrogen management had a considerable impact on the growth, production, nodulation, and nitrogen concentration of jack beans. The sole jack bean receiving 100% of the recommended N (T2) exhibited the significantly highest plant height (108.75 cm), number of pods per plant (11.63), seeds per pod (7.70), and seed yield (899 kg ha−1), whereas the shisham–jack bean system with 100% recommended nitrogen (T5) yielded a similar seed output of 876 kg ha−1. Rhizobium-inoculated shisham–jack bean without mineral nitrogen (T6) showed the most significant nodulation (37.35 nodules per plant), nodule dry weight (303.25 mg plant−1), seed nitrogen concentration (2.98%), soil NH4+-N (10.15 mg kg−1) and NO3−-N (6.68 mg kg−1). Total nitrogen concentration by plants was significantly highest in T5 (53.63 kg N ha−1) and was statistically at par with T2 and T6. The growth and biomass accumulation of shisham were similarly maximized in T5, which achieved a tree height of 5.31 m, a diameter at breast height of 8.99 cm, and a total biomass of 9.60 Mg ha−1. The findings indicate that suitable mineral nitrogen supplementation augmented productivity in the shisham–jack bean system, but Rhizobium inoculation enhanced nodulation and was associated with greater plant N concentration and soil mineral N under zero mineral-N conditions.
